1. Field of the Invention
The present invention relates to a control unit for mixed light illumination, especially for control of LED lighting devices of a microscope, stereomicroscope, macroscope and industrial image processing and/or vision machine. For simplicity in the following the term “microscope” is used in some cases for the foregoing devices in the specification below.
2. Description of the Related Art
The optimum illumination of objects to be examined plays an important role in microscopy. Whether accurate images or shapes are to be detected by an observer or automatic image analysis system generally depends on the illumination. Stereomicroscopy puts especially high requirements on the quality of the illumination. In that area exactly point-wise production of light and shadow often occurs. The more accurately the incident light falling on the object is controlled, the more information can be obtained by microscopic examination of the object.
Illumination used in microscopy is generally divided into two basic classes, incident light illumination and transmitted light illumination. In each of these classes bright field illumination and dark field illumination are distinguished from each other. Each of these types of illumination may be again divided. For example, incident light-bright field illumination includes shadow-free incident light inclined incident light, vertical incident light, coaxial incident light, diffuse incident light, etc. Each of these types of illumination produces certain light-shadow conditions and thus the desired contrast of the object being examined.
Fiber optic and LED illumination systems are established as illumination sources. Fiber optic illumination systems generally include cold light sources and various light guides connected to a light source. Different types of light guides are known to provide the above-described types of illumination. DE 198 20 012 C1 describes a fiber-optic transmitted light device for producing bright field illumination in transmitted light. This device has a cold light source connected to a light distributing body formed as a hollow chamber by means of a light guide. The input end of the light guide is connected to the cold light source and the output end to the light distributing body. Further examples fiber optic illumination systems include split or multipoint ring guides for producing a shadow-free bright field illumination in incident light, dark field guides for producing a shadow-free dark field illumination in incident light, multi-armed point light guides for producing inclined incident light with a predetermined adjustable incidence direction and linear guides for lateral bordering incident light dark field illumination with inclined shadows.
The LED illumination systems are preferred for use in the industrial image processing area with automated image analysis system. In these systems a number of LEDs is usually built into an LED illumination head, which are designed according to the above-described illumination types. Also ring guides, spot guides, linear guides, etc., are provided. In contrast to fiber optic illumination systems, in which light must be guided to the illumination head, each LED in the LED illumination head becomes an individual light source, when it is supplied with electric current.
The long service life of the LEDs in comparison to the halogen reflector lamps generally used for the cold light source is an often stated advantage of the LED illumination systems in contrast to the fiber optic illumination systems. However reduced brightness and less compact structure for the LED illumination heads are substantial disadvantages for the LED illumination systems in contrast to the fiber optic illumination systems.
The simpler electronic control of the LEDs is a decisive advantage of the LED illumination systems over the fiber optic illumination systems. Use of LED illumination for microscopic applications is increasing because of this advantage. U.S. Pat. No. 5,690,417 described an LED ring guide, with which individual LED groups can be controlled, e.g. arranged as circular or ring light segments. The incidence direction of the light in inclined incident light may be changed by control of these segments. Suitable control of the ring light segments in a predetermined sequence can produce the impression of a light rotating around the object. This type of moving illumination can help to obtain a better impression of the three dimensional shape of the object. Fiber optic illumination systems can control individual segments of lighting units only with considerable mechanical effort and expense. Segment control has not been commonly used for fiber optic systems for this reason.
The desired control of individual LEDs in LED illumination systems is often accomplished by means of digital control signals. In EP 1 150 154 A1 the use of a microcontroller for handling the control statements is suggested.
It has been shown that the known illumination systems for many application purposes are insufficient. Especially it is often desirable to be able to observe objects with the help of mixed light, i.e. incident light from different lighting units or illumination devices at the same time, for example using both incident and transmitted light at the same time.
The term “lighting unit” or “illumination device” means each standalone controllable combination of light sources mounted in a common housing for illumination of an object. An illumination system is at least one lighting unit or illumination device in combination with a control unit for control of the lighting unit or illumination device and/or the current associated with it. An example of an illumination device or lighting unit is an LED ring light and an example of an illumination system is the integrated LED ring light of EP 1 150 154 A1.
If mixed light observations are made with the available prior art systems, several LED illumination systems must be combined, for example a LED ring light for incident light production and an LED transmitted light source. The user must adjust each of these illumination devices or lighting units, i.e. its intensity, selected segments, etc., according to the structural conditions of the object to be observed. When the same object must be observed still later, often time consuming new adjustments of the illumination conditions must be performed. Their reproducibility is problematical, time consuming and often depends on the cleverness of the user. Furthermore currently each lighting or illumination device in these combinations of illumination systems has its own current and /or control unit, so that the total system takes up a comparatively large amount of space and is expensive.